1. Field of the Invention
The present invention relates to a wind turbine blade, and especially relates to a wind turbine blade preferably used for wind power generation and to a manufacture method thereof.
2. Description of the Related Art
One property required for wind turbine blades is lightweight with sufficient strength. This is important especially to provide large and long wind turbine blades (for example, a length more than 20 meters). To increase the length of a wind turbine blade, the structural strength of the wind turbine blade is required to be sufficiently high. However, the weight increase accompanied by the strength enhancement causes a mechanical load to be applied to the structure supporting wind turbine blades (for example, a nacelle and a tower). For example, a wind turbine blade having a high strength and also an excessive weight cannot be actually employed for a wind turbine.
The spar cap structure is a wind turbine blade structure which is currently widely used to satisfy both requirements of lightweight and strength. The spar cap structure is disclosed, for example, in Tony Burton et al., Wind Energy Handbook, John Wiley & Sons, LTD. U.K. 2001, December, P. 380. FIG. 14A is a cross sectional view showing the structure of the wind turbine blade disclosed by Burton. The disclosed wind turbine blade 10 includes an outer skin layer 101, spar caps (main structural members) 102, lightweight core members 103, and share webs (beam members) 105. One spar cap 102 is provided on each of dorsal and ventral sides of the wind turbine blade 100. The outer skin layer 101 and the spar caps 102 are both formed of fiber-reinforced plastics. On the other hand, the lightweight core members 103 are formed of resin foam such as the PVC or a lumber such as balsa wood. As shown in FIG. 14B, the lightweight core members 103 are sandwiched between the outer skin layer 101 and an inner skin layer 104. In this structure, the strength of the wind turbine blade 100 is mainly maintained by the spar caps 102 formed of fiber-reinforced plastic. The lightweight core members 103 are collaterally used for ensuring the strength. The spar cap structure realizes a wind turbine blade which is lightweight and highly strong by providing the spar caps 102 for ensuring the strength, without increasing the overall thickness of the outer skin layer 101.
The above-described spar cap structure definitely satisfies the requirements for lightweight and sufficient strength to a certain extent. However, a recent wind turbine requires wind turbine blades to be further large and long. In addition, it is increasingly required to manufacture a wind turbine blade at a low cost. It has been becoming difficult for the wind turbine blade employing the spar cap structure to satisfy such requirements.
From such backgrounds, there is a need for a structural design of a wind turbine blade which satisfies both requirements of lightweight and strength at a high level, preferably at a low cost.